Adult sintervos are still fairly small creatures, the size of regular foxes if they were stretched. Their patterns begin to come in about a year after they hatch, bright gold for the males and green for females. They waste no time preparing for their first solstice as adults, scurrying around the Keep searching for small trinkets to gift. They are still quite elusive, most magi only catching brief glimpses of the creatures during the entire season as they turn a bend or disappear up a chimney. Their caretakers, however, are well aware of them this time of the year, as the creatures regularly return to their magi's room to see if their magi has presents for them to deliver. The foxes are so good at ferrying gifts around, even to remote corners of the world, that keeping up with their desire to gift can be difficult. The foxes, as well as being nimble and swift, have the unusual ability to turn large objects into little ornamnets and baubles. When they have a lot of gifts to deliver, they'll simply fasten these baubles to their fur and dash off, looking very much like an animate Solstice tree. Their sense of direction is impeccable and they can even deliver gifts to people on remote islands and be home by nightfall. No one is quite sure how they do this, as rumors sintervos can fly have never been verified.

Winter is a rough time of year in the north, with light vanishing for days at a time and many creatures gone much further south to wait out the colder, snowier nights. However, even in the far north, people find ways to cheer themselves up with tales about the sintervos. These creatures are incredibly shy, considered little more than a myth even by the denizens of Synara and other major cities, but the northern folk of the Arkene still take care to leave milk and crumbs next to the fireplace in the winter for the sintervos. Parents often tell their children that the sintervos is invisible throughout the year, occasionally checking in on households to see if the children are behaving. On the Solstice, the sintervos become visible and get to work delivering presents to those who were good throughout the year. If the children were bad, their parents warn they'll be visited by cruel demon creatures that like to destroy presents instead.